* {
  margin: 0;
  padding: 0;
}
body {
  display: flex;
  flex-direction: row;
  justify-content: center;
  align-content: center;
  height: 100vh;
  overflow: hidden;
}
.container {
  display: flex;
  width: 90vw;
}
.container .panel {
  height: 80vh;
  flex: 0.5;
  border-radius: 50px;
  color: #fff;
  cursor: pointer;
  margin: 10px;
  position: relative;
  background-size: cover;
  background-position: center;
  background-repeat: no-repeat;
  transition: all 700ms ease-in;
}
.container .panel h3 {
  font-size: 24px;
  position: absolute;
  left: 20px;
  bottom: 20px;
  margin: 0;
  opacity: 0;
  transition: opacity 300ms ease-in 400ms;
}
.container .panel.active {
  flex: 5;
}
.container .panel.active h3 {
  opacity: 1;
}
@media (max-width: 480px) {
  .container {
    width: 100vw; /* 修复：添加冒号 */
  }
  .panel:nth-child(4),
  .panel:nth-child(5) {
/* 修复：用逗号分隔 */
    display: none;
  }
}
